line and phase voltage

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Answers based on the 2008 & 2011 NEC.

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line and phase voltage

sir
i have seen (snip) 120/240 for houses: 120 is line to ground, 240 is line to line

so got the point from this point that we have three phase connection so
120 is phase voltage and 240 is line voltage

but line voltage is=squareroot of 3 *phase voltage and (240 is not equal to sqroot of 3*120)
(snip)

If you indeed had two legs of a symmetric neutral (wye; star; etoile) 3 phase system as your service then hot to hot would measure about 208 volts.

Once in awhile, residences in (upper floors of?) a commercial building or in a primarily commercial district may have 120/208 volt service taken from 3 phase pole transformers. In general, 120/240 rated and 240 volt only rated equipment may not be connected to 120/208 volt systems and vice versa. Some equipment is rated for both voltages.

A 120/240 volt 3 phase system (it's always 3 phase delta) provides 120/240 volt single phase power per the diagram above and a third hot wire is for 240 volt only 3 phase equipment such as machinery,

Even in a three phase system of any kind, if you take power from any two terminals (hot and hot, or hot and neutral) you will have a single phase source.

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line and phase voltage

line and phase voltage

sir
i have seen on this site------------------------------------------------------------120/240 for houses: 120 is line to ground, 240 is line to line

so got the point from this point that we have three phase connection so
120 is phase voltage and 240 is line voltage

but line voltage is=squareroot of 3 *phase voltage and (240 is not equal to sqroot of 3*120)
please send the answer on --------- as soon as possible

If your hot to neutral is measured at 120v !
Then the voltage across two hots depends on two things !
If it originates from a split supply then it will be 240v !
But if it is a measur ment from two phases,
of a three phase supply,
then it will not be 240v! but more like 220v,
Because the phase difference in a three phase system
would be only 120 degrees,
Where as in a split supply it would be 180 degrees.

If you are tring to understand electrical systems,
Then you must understand the difference between
split systems and three phase systems !

line and phase voltage

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__________________
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
Answers based on the 2008 & 2011 NEC.